Colin River, Belfast

It rises on Black Mountain, the hills to the north west of the city of Belfast.

The source is on top of the Antrim Plateau and so is actually quite flat.

The geology here is basalt, laid down 60 million years ago as the Atlantic Ocean began to form.

It then flows down through a steeper valley called a glen (the Colin Glen), which is the location of an ancient fault.

As it erodes vertically down, it cuts down through our geological history, first revealing limestone formed by the deposition of shells & skeletons of tiny sea creatures 80 million years ago (green) before flowing into an area of even older mudstone (orange).

The mudstone is very soft and erodes very easily.

The river then levels off a bit, flowing through some more areas of mudstone before entering the River Lagan

The Colin River also is an interesting river as it flows through both rural and urban areas. Let's explore that using this landuse GIS layer.

Near the source it flows through an area of upland grass (pale green). There are very few trees here. So, when the rain falls on the hills, there is less interception and the water travels to the river fast.

This means the discharge levels can go up and down very quickly (a river that does this is called a spate river).

As we move down into the Colin Glen, the landuse pattern is interesting.

The immediate surroundings of the river is a wooded glen (stronger green), managed in a reasonably natural state.

However, just outside that, the river has moved into the urban area of the suburbs of West Belfast (red). So, just beyond the trees there are lots of impermeable surfaces - roads, buildings, pavements - and drains. This means that a lot more water flows into the river fast here.

The final stretch of the Colin River, as it flows down to the confluence with the Lagan, travels through an urban area. In fact, at times the river is covered over entirely (culverted) and is not visible.